Recently, the ophthalmic arts have experienced an increasing acceptance and demand for contact corrective lenses which are fitted directly to the eyeball of the wearer to effect optical correction therefor. This demand has resulted from many considerations, such as cosmetics, convenience, etc., unaffordable by standard eyeglasses. Notwithstanding the broad base of acceptance of such ophthalmic devices, certain ingenerate problems with these systems have arisen, particularly in view of the proximity of the corrective device to the very sensitive eyeball.
The first, most widely employed contact lens may be described as the hard lens which is a rigid, ground glass or optical grade plastic (polymethylmethacrylate) individually fitted to the wearer's eye. While these hard lenses are capable of providing exacting optical correction, by virtue of their hardness and lack of resilience, they pose certain significant problems to the wearer. Most notably, due to their rigidity, the cornea of the eye is forced to adapt to the concave topography of the corrective lens, which may result in significant discomfort during the initial period of wear. Moreover, it is well known that this variety of corrective contact lens is highly susceptible to dislodgment and possible loss from even simple eyeball movements. Such problems have become increasingly more pronounced as the diameter of these corrective lenses have been reduced to a size approaching that of the pupil.
In response to the various inherent deficiencies manifested by the hard-type contact lenses, soft, hydrophilic lenses have experienced increasing popularity. In contradistinction to the hard lenses, these hydrophilic lenses are very supple and resilient in their hydrated condition. Accordingly, they will adapt to the exterior topography of the cornea and, being generally larger in diameter than hard lenses and typically covering the cornea as it is defined at the peripheries thereof by the sclera, will add to the pressure on the limbus. By virtue of these characteristics, the ease of wear is considerably enhanced while the frequency of dislodgment is similarly reduced. However, there are yet other significant problems posed by these semi-scleral, hydrophilic ophthalmic devices.
The most notable shortcoming of the soft, hydrophilic lenses currently marketed for optical correction centers about reduced fluid and oxygen permeability therethrough. As noted above, this type of lens typically covers the entire corneal region effectively masking same from the atmosphere. It is well known that the outer surface of the eyeball requires both lubrication and oxygen for proper health and that lack of these essentials promotes, for example, edema. Currently, these rather large corrective devices often result in eye irritation to the wearer as the result of interference with the ordinary lubrication and oxygen demands of the eyeball. Presently, these hydrophilic devices rely primarily upon conditions established in and under the flexible lens and when the wearer blinks to allow tear fluids to wash between the outer surface of the cornea and inner, concave surface of the lens, thus providing some minimal amount of lubrication. Additionally, as the tear fluid is drawn behind the lens, some oxygen entrained in the fluid will similarly be caused to pass between the cornea and the lens. However, the ability of this system to provide adequate volumes of both lubricating tear fluid and oxygen are highly unsatisfactory. Such problems necessitate frequent removal and restricted periods of wear to permit regeneration and repair of the tissue.
These deficiencies have been recognized for decades. Note, for example, U.S. Pat. No. 2,393,266 to Riddell which is directed to the concept of providing a plurality of perforations in the peripheral areas of these scleral lenses to promote lubrication of the eye. Many techniques have been developed to achieve these ends, those most notable being conventional drilling and trephining as well as the more recent techniques of laser drilling. See, for example, U.S. Pat. No. 3,688,386. Each of the aforementioned, however, has proven unsatisfactory for one or more reasons. The conventional drilling or trephining techniques yield perforations, more properly termed fenestrations, which are of relatively large diameter and exhibit intolerable roughness both along the surface of the lens as well as the interior dimensions of the fenestration. Laser techniques have shown some promise; however, the expense involved to achieve even a minimal number of fenestrations has proven prohibitive. Regardless of the fenestration producing technique employed, i.e., conventional or laser drilling, system limitations per se provide inadequate results. Since each is fundamentally based upon mechanical systems to effect alignment and production of the fenestrations, the lower limit of fenestration diameter as well as the distance between adjacent fenestrations is significantly restricted. Ideally, fenestrations for ophthalmic lenses should exhibit diameters of 0.001 inch or less and be present in a density sufficient to allow for 100-150 fenestrations about the periphery thereof. Currently, no technique exists to achieve these results. Accordingly, the need exists to simply, yet efficiently provide fenestrated hydrogels suitable for use as corneal or scleral, corrective ophthalmic devices.